Field of the Invention
The invention relates to a circuit configuration for detecting a functional disturbance having a first and a second differential amplifier, the outputs thereof being connected to the inputs of a gate, one input in each case being connected to a reference potential terminal and the other input in each case being coupled to the supply voltage.
In the event of low-frequency voltage fluctuations in the supply voltage, the functionality of an integrated circuit generally remains ensured. However, an undefined state of the integrated circuit can arise in the event of high-frequency disturbing pulses. By way of example, the synchronization of different signals of the integrated circuit can be disturbed.
A memory content could be read out erroneously. Equally, logic circuit configurations could be adversely influenced.
These intrinsically undesirable effects can be exploited, however, in order to discover the structural construction and the method of operation of an integrated circuit.
In order to prevent such fraudulent intentions, voltage fluctuations within a specified supply voltage range are masked out by filter circuits. In this case, however, the integrated circuit does not generally interrupt its functional sequence.
It is accordingly an object of the invention to provide a circuit configuration for detecting a functional disturbance which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which prevents, or at least detects, functional disturbances of the abovementioned type in an integrated circuit.
With the foregoing and other objects in view there is provided, in accordance with the invention, a circuit configuration for detecting a functional disturbance, comprising:
a supply potential terminal;
first and second differential amplifiers each having an output;
a gate with inputs respectively connected to said outputs of said first and second amplifiers;
said first and second differential amplifiers each having a first input connected to a reference potential terminal and a second input connected to receive a supply voltage; and
a monitoring device connected to said second input of each of said first and second differential amplifiers for responding in an event of a change in a supply voltage at said supply potential terminal.
The invention exploits the fact that a circuit configuration which monitors voltage fluctuations in the supply voltage is generally present in each integrated circuit. Integrated circuits can be operated within a predetermined supply voltage range. If the supply voltage exceeds an upper voltage threshold or if the supply voltage falls below a lower voltage threshold, then a so-called xe2x80x9cpower on resetxe2x80x9d is triggered. This means that the integrated circuit is brought to a defined operating state after the triggering of a xe2x80x9cpower on resetxe2x80x9d. Thus, this functionality is utilized for example to trigger a power on reset whereby the integrated circuit during switch-on on account of a supply voltage rising continuously from zero, upon reaching the lower specified voltage threshold, which power on reset then switches the integrated circuit into a defined operating state. By way of example, two voltage dividers are provided for setting the lower and upper voltage thresholds, which each trigger the power on reset. The voltage divider which defines the upper switching threshold is connected to one input of the first operational amplifier, while the voltage divider which defines the lower switching threshold is connected to one input of the second operational amplifier. The respective other inputs of the first and second operational amplifiers are connected to a reference potential terminal at which a fixedly set reference voltage is present. The outputs of the first and second operational amplifiers are fed to a gate which evaluates the signal supplied by the first and second operational amplifiers and makes it available at an output. The output of this circuit configuration is connected to another circuit region of the integrated circuit, which can then trigger the power on reset.
However, since this circuit configuration for detecting a voltage fluctuation is not suitable for detecting high-frequency voltage fluctuations ranging within the reset thresholds, the invention provides for the respective other input of the first and second differential amplifiers to be connected to a monitoring device, which responds in the event of a change in the supply voltage at a supply potential terminal of the circuit configuration.
A monitoring device or monitoring means is preferably assigned to each differential amplifier.
The monitoring device may be embodied as a differentiator, for example. However, it may also be a charge storage device or accumulator connected to the supply potential terminal. The rates of change of the supply voltage at which the respective operational amplifier is to respond can be set depending on the dimensioning of the monitoring means. Preferably, the components are dimensioned in such a way that only high-frequency voltage changes in the supply voltage are detected. In this way, it is possible to prevent a disturbance in which the supply voltage fluctuates beyond acceptable thresholds which would cause functional disturbances in the sequence of the integrated circuit. Since low-frequency voltage changes generally do not impair the sequence of the integrated circuit, the monitoring means does not have to respond, in other words exceed the reference voltage which is present at the aforesaid one of the inputs of the first and second operational amplifiers.
In a preferred refinement, a voltage divider is provided between the supply potential terminal and a reference-ground potential terminal, the center tap of which voltage divider is connected to the respective monitoring means and the respective differential amplifier. As mentioned in the introduction, the voltage divider serves for setting the upper and lower voltage thresholds. Consequently, a dedicated voltage divider is provided in each case both for the first and for the second differential amplifier.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a circuit configuration for detecting a functional disturbance, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.